A. It is not known whether central or peripheral adaptations are primarily responsible for the markedly increased aerobic performance of endurance trained older men relative to their sedentary age peers. To answer this question, we performed maximal upright cycle ergometry in 16 endurance trained men 63+/-7 yr old and 35 untrained men of similar age from the BLSA. During cycle ergometry, trained men achieved higher maximal workloads, WL, (177+/-28 vs 131+/-28 watts, p less than .0001) and higher peak VO2 (34.2+/-3.6 vs 22.3+/-5.8ml/kg/min, 0 less than .0001). The higher peak VO2 in trained men was achieved by a 22.5% higher cardiac index, CI, (9.8+/-1.9 vs 8.0+/-1.5l/min/m2, p less than .001) and a 16.5% greater arteriovenous O2 difference (13.3+/-2.6 vs 11.5+/-3.0 vol/100ml, p less than .05). The higher maximal CI in the athletes was mediated entirely by a higher stroke volume index, SVI, (68.7+/-10.5 vs 57.5+/-11.3ml/kg/m2, p less than .002). Thus, the augmented aerobic capacity of endurance trained older men during upright cycle exercise (EX) is achieved by both central and peripheral adaptations, which are of similar magnitude. B. It has been hypothesized that age-associated reductions in physical conditioning status mediates the decrease in LV early diastolic performance seen with advancing age. To test this hypothesis, we measured radionuclide ventriculographic peak filling (PF) rates at rest and throughout graded maximal upright cycle ergometry in 56 sedentary BLSA men and 12 highly trained old men. At rest, at 50% of maximum WL and at maximal effort, PF rates declined with age but were similar in older athletes and their sedentary age peers. These results suggest that the age-associated decline in early diastolic filling (DF) observed at rest and during EX cannot be reversed even by intensive long-term endurance training. C. To determine the effect of deconditioning on LV DF in endurance trained older men, 9 such men underwent serial radionuclide ventriculography at rest and during maximal upright cycle EX before and after 12 weeks of deconditioning. Although resting PF rates and cardiac volumes did not change significantly after deconditioning, at peak EX WL, PF rate (893+/- 197 vs 1124+/-319ml/ sec, p less than .05) as well as end- diastolic volume index (73+/-13 vs 84+/-17, p less than .05) and SVI (59+/-11 vs 71+/-14ml/m2, p less than .05) were reduced after deconditioning. These findings suggest that the decrease in LV volumes at peak EX seen after deconditioning in highly trained seniors may be mediated by a reduction in diastolic early PF rate.